#1 the brown dots and specs in the surface are from burned bits of ABS that are attached to the side of the hot nozzle and drip down into the print. Caution, while some of that just happens normally, you also want to ensure you do not have a hotend leak- caused by improper hotend assembly. That can make a real mess of a hotend and is simply a failure to tighten the nozzle against the throat tube to form a metal to metal seal inside the heater block. While this older topic is for the previous N series, I highly recommend you read this topic and all replies to ensure you understand what a hotend leak looks like (yours are covered by the white silicone socks on a Pro2). viewtopic.php?f=4&t=6599&p=26953&hilit=leak#p26953This is the Pro2 series specific nozzle and hotend official documents, but also good to see and learn from others and previous mistakes and failures.https://cdn.shopify.com/s/files/1/1069/ ... 2358962206https://cdn.shopify.com/s/files/1/1069/ ... 2358962206

#2 ABS is a high shrinkage and prone to warping material. It shrinks up to 3% as it cools from hot liquid out of the nozzle to solid plastic as the layer. In order to limit and combat this shrinkage and warping, we keep the entire area around the printing object warm, by both the bed heat and the ambient hot air around the part. When you see a change like this, it is most likely related to something ambient changing. Example is printing lid off or lid on. Door open or closed. Ambient room temp changing. Other factors that are settings are the print layer cooling fans and ducts on or off or changes. Note the layer cooling fans are different than the extruder cooling fan on the front of the extruder that cools the heatsink above each hotend.

Shelton wrote:Clogged nozzle? Try to replace it first or clean it... But I'm not sure for 100%.

No, this is not a clogged nozzle, not in the slightest. Do not touch or take apart a nozzle or hotend unless you have no other option. Just telling you now before you start buying $80 a piece hotends for no good reason and mistakes.

Pillowing show up as bumps in the top surface of a print and can either be open or closed. The most important thing here is to make sure that your cooling fans are going top speed when the printer is laying down the top layer. Without proper cooling the thin strands of plastic tend to curl up and stick up above the surface of the print and make it harder for subsequent layers to properly span over the gap. With good cooling the strands gradually grow over the gaps until it closes fully.

Besides cooling you also need to print a thick enough top surface so that the printer can properly close it. In general you should make sure that you are printing at least six top layers. Since the top and bottom thickness is set in mm you will have to do some basic math to make sure you're printing enough layers. If you are printing with a 0.1mm layer height you should make your top thickness at least 0.6mm.

In general you will need more top layers the thinner your layer height is. With very thin layers the thin strands of plastic are more likely to break before fully bridging over the gaps in the infill and providing a nice base for the following layer. You will therefore need to print more layers to make up for this. In other words very thin layers can be another cause of pillowing.

Keep in mind, you are printing ABS- a high shrinkage material that requires careful control of ambient heat and airflow around the print.I'm saying this, because the above advice of print layer fan blowing full blast 100% cooling may not be the best or correct answer for that print and ABS. I'm just trying to convey to you that again, in some way, something with airflow and ambient temp is different and that explains why this printed before and is potentially now getting slight pillowing over the infill. You will have to experiment and find the best settings.